IT201600093143A1 - METHOD FOR THE REDUCTION OF THE ORGANIC CONTENT OF THE LANDS OBTAINED IN THE FORM OF EXCAVATION MECHANIZED FOR THE REALIZATION OF GALLERIES AND WELLS - Google Patents

Description

"METHOD FOR THE REDUCTION OF THE ORGANIC CONTENT OF THE LAND OBTAINED DURING THE MECHANIZED EXCAVATION PHASE FOR THE CONSTRUCTION OF TUNNELS AND WELLS"

The present invention relates to the use of the oxidative process based on Fenton reagents for the treatment of earth excavated by means of a mechanical cutter. This treatment can be used to reduce the organic content, in particular to reduce the content of anionic-cationic and non-ionic surfactants, used in the conditioning phase of the ground during the mechanized excavation of tunnels and wells.

State of the art

Currently, tunnel excavation can be carried out using two main technologies:

use of explosives or classical method;

through the use of mechanical means.

The first method involves the cyclic application of the following operations that allow the progress of the route:

1) By means of an automatic drilling machine called Jumbo, a series of holes is made on the excavation face which are filled with explosives; both the arrangement of the holes and the quantity of explosive are calibrated in order to break down the desired portion of rock, without causing damage to the portions of rock that will act as natural support for the excavation; 2) The resulting material (called spoil) is removed with mechanical shovels and trucks;

3) The excavation is supported with specific technologies, such as the application of ribs and shotcrete and riveting.

The method is based on the elimination of the right portion of rock, so as to achieve a re-distribution of forces around the excavation known as the arch effect which partially supports the consolidating action of the reinforcements and shotcrete.

The second construction technique can be divided into two broad categories, depending on whether the excavation takes place in partial or full section sections (i.e. excavating the entire section of the tunnel at the same time). In the first case, proceed as already described for the traditional method with punctual cutters and with breakers (instead of explosives), gradually creating the shape of the tunnel which is then covered with reinforced or non-reinforced concrete depending on the geological conditions. . In the second case, the advancement is carried out with a complex machine called TBM (Tunnel Boring Machine), also known as "milling machine" or "mole", which, in addition to carrying out the excavation, is able to support the excavation face (of consequently avoiding subsidence of the front and possibly of the ground level), to transport the spoil outside (by means of an auger, a conveyor belt and / or special wagons) and to put in place the final lining which is generally made up of precast concrete segments armed. This type of machine is able to excavate almost all the existing geological contexts, from compact rock (hard rock cutter) to fractured rock (double shield cutter), up to loose soils, below the aquifers and with low roofing with the use of TBMs capable of applying a counter pressure to the excavation face: EPB - Earth Pressure Balance machine, Slurry Shield, Hydro Shield, hybrid TBMs.

Broadly speaking, a TBM cutter is made up as follows:

1) A rotating head, i.e. the front part in direct contact with the face, equipped with a series of tools depending on the geology of the excavation, which serves to excavate, support the face, collect and convey the spoil towards an evacuation system.

2) An excavation chamber placed between the head and the transport system of the spoil (in the case of TBM with counter-pressure system at the face), in which the excavated material is collected. In the case of EPB, the material exits the chamber on an auger, or worm, and is placed on a conveyor belt.

3) A transport system of the spoil towards the outside of the tunnel (for example a conveyor belt or wagons).

4) A system for the installation of the tunnel lining, generally precast concrete segments.

The milling head mounts tools of various types and sizes and is designed according to the geology to be excavated. The tools are generally of three different types: “cutters”, “scrapers” and “rippers”.

In the case of TBM with counter-pressure system at the face, the advancement can take place with the excavation chamber constantly and completely full of the extracted material, suitably conditioned, in order to guarantee a homogeneous and uniform distribution of earth pressure at the face and without pressure drops between one push and the next. In some cases, depending mainly on the geological and hydraulic conditions, it is possible to advance with the excavation chamber empty or partially full of extracted material.

In EPB, rock or hybrid TBMs, it is common practice to apply a conditioning agent to the excavated soil or rock, in different positions of the TBM: excavation face, excavation chamber and extraction screw.

Known stabilizing agents include bentonite and polymeric suspensions. These can lead to problems, because they significantly increase the water content of the soil, obtaining very liquid systems that are difficult to extract from the chamber and difficult to manage when transferring the excavated material to authorized sites.

In the latest developments of this technology, polymer foams have been used. These have the considerable advantage of significantly reducing the amount of water in the soil. A standard polymer foam formulation comprises a foaming agent and a stabilizing agent.

During the operation of the TBM, the foam is injected in different positions: directly to the face through special nozzles positioned on the excavation head, inside the excavation chamber and in the auger.

The application of foam as a conditioning agent has a number of benefits: homogenization of the soil, control of groundwater, greater speed of advancement and ease of extraction of the excavated material, minimization of the adhesion properties of some soils (for example, clays can cause adhesion problems to metal surfaces, thus making excavation operations slower or even impossible), etc.

The injection of these foaming agents leads to an increase in the concentration of the organic content of the excavated matrix, making the storage procedure of the excavated material, both temporary and definitive, difficult to manage. In fact, long storage periods can be envisaged to promote a natural biodegradation of the organic components used in the conditioning phase. In the current state of the art, to reduce the storage times of conditioned lands, washing systems with water are provided to extract the contaminant and subsequent chemical and / or biological treatment of the wastewater obtained.

US 20150021275 describes a method of decontamination of the soil and groundwater in which solutions of hydrogen peroxide and carboxylic salts are injected through wells which react with the iron naturally present to reduce the organic content.

US 8178742 describes a method for the in situ remediation of areas contaminated by organic compounds, such as aliphatic oils, chlorinated solvents and aromatic compounds, by injecting a chelating agent and, after 6 - 48 hours, a stabilized hydrogen peroxide solution.

US 5716528 describes a process for the removal of organic compounds from contaminated water using hydrogen peroxide as oxidant in the presence of a catalytic quantity of ferrous ions. The pH is indicated as an important parameter, which must be acidic to promote the oxidative degradation of contaminants such as polycyclic aromatic hydrocarbons and / or aromatic compounds selected from the group of phenols and chlorinated phenols.

EP 1473278 describes a process for the purification of waste water, in particular from landfills or industrial processes, characterized by a catalytic oxidation by hydrogen peroxide in combination with the addition of divalent iron and / or trivalent iron ion and subsequent alkaline neutralization with sodium hydroxide or milk of lime.

Description of the invention

The present invention relates to the oxidative treatment based on the use of Fenton reagents, hydrogen peroxide and Iron (II) ions, in order to reduce the organic content of the earth from mechanized excavation in a significantly faster way than practically until to date.

The invention provides a method for reducing the organic content, in particular the surfactant content in the soil which includes the addition of the reagent (s) inside the tunnel (on the excavation face and / or in the conditioning chamber and / or in extraction screw and / or on the extraction belt and / or on the transport wagons) and / or outside the tunnel (vats and storage areas of the excavated material). Furthermore, the method of the invention can be used to reduce the organic content of stored earth deriving from the mechanized excavation process with a cutter.

Surfactants are used during the excavation phase at the face, in the excavation chamber and in the auger to condition the ground, to allow faster advancement and extraction of the same and to maintain the stability of the excavation face. Surfactants can be anionic, cationic and non-ionic in nature.

The method of the invention provides for the use of hydrogen peroxide in aqueous solution and a source of iron (II) ion. Iron (II) ions, if not naturally present in the soil, are supplied as ferrous sulphate. The invention also has as its object the use of hydrogen peroxide and Iron (II) salts for the reduction of the content of organic compounds in the ground excavated by means of mechanical cutters for the construction of tunnels and wells The percentage of hydrogen peroxide, expressed as a percentage by weight of a 5% hydrogen peroxide solution by volume, it can vary from 0.1% to 15.0% expressed on the quantity of soil.

The quantity of iron (II) ions, expressed as a percentage by weight of ferrous sulphate heptahydrate, can vary from 0.01% to 10.00% expressed on the quantity of soil. The source of Iron (II) ions necessary to promote the oxidative reaction may be naturally present in the soil to be treated.

The method of the invention is particularly efficient for reducing the content of anionic surfactants in the soil, in particular of surfactants of the alkyl sulfate or lauryl sulfate salt type such as sodium salts of lauryl sulfate with an ethoxylation number of 7.

The characteristics and advantages of the treatment of the invention are better described in the following examples. The content of anionic surfactant is expressed as mg of surfactant contained in a kilogram of soil. The determination was carried out through spectrophotometric analysis with the MBAS method (Methylene Blue Active Substances), reading the absorption at 650 nm. In cases where a high interference in the MBAS method by the extracted soil was noted, it was decided to express the data as absorption at 650 nm.

The absorption at a wavelength of 650 nm is characteristic of the blue molybdenum-anionic surfactant complex.

Example 1

Table 1 shows the dosages, expressed as a percentage by weight on the soil, of hydrogen peroxide at 5% in concentration and ferrous sulphate heptahydrate used for the treatment of soil conditioned with anionic surfactant.

Parts by weight referred to the quantity of soil (%)

Treatment Treatment Treatment Treatment Treatment 1 2 3 4 5

Water 0.40 0.80 1.60 2.67 3.87

oxygenated

5%

Sulphate 0.07 0.13 0.27 0.43 0.63

ferrous

heptahydrate

Water 16.70 16.70 16.70 16.70 16.70

Table 1: composition of treatments

The conditioned reference matrices to be treated are prepared by adding 85 mg of sodium laurylethoxy sulfate and 167 g of water to each kilogram of medium. To obtain homogeneous and conditioned matrices, they are mixed with a mechanical stirrer. These conditioned reference matrices are treated with variable quantities of hydrogen peroxide (5% concentration) and ferrous sulphate heptahydrate. After 24 hours from the treatment, the matrices are extracted with water and the elutriates obtained are treated as described in the method for the determination of anionic surfactants according to the MBAS technique. Finally, the absorption, through a spectrophotometric technique at 650 nm, of the final solution obtained by complexation with molybdenum blue and extraction in chloroform is evaluated. The data obtained by analyzing the soil as it is and the conditioned reference matrix are used as reference values.

Absorption at 650 nm

Reference soil 0.03873

Reference matrix <0.10500>

Treatment 1 0.10926

Treatment 2 0.08721

Treatment 3 0.058280

Treatment 4 0.03437

Treatment 5 0.03449

Table 2

The data shown in Table 2 and Figure 1 show a reduction in absorption by increasing the dosages of hydrogen peroxide (concentration 5%) and ferrous sulphate heptahydrate. Treatments 4 and 5 show an absorption comparable to the value obtained by analyzing the soil as it is. It can be inferred that the surfactant in these treated matrices is completely degraded.

Example 2

Table 3 shows the dosages, expressed as a percentage by weight on the soil, of hydrogen peroxide at 5% in concentration and ferrous sulphate heptahydrate used for the treatment of soil conditioned with anionic surfactant.

Parts by weight referred to the quantity of soil (%)

Treatment Treatment Treatment

6 7 8

<5% hydrogen peroxide> 10.67 10.67 40.00

Ferrous sulphate 0.63 0.00 0.00 heptahydrate

Water 16.70 16.70 16.70

Table 3: composition of treatments

The matrices to be treated are prepared by adding 85 mg of sodium laurethoxy sulfate and 167 g of water to each kilogram of reference medium. To obtain homogeneous and conditioned matrices, they are mixed with a mechanical stirrer. These conditioned matrices are treated with variable quantities of hydrogen peroxide (5% concentration) and ferrous sulphate heptahydrate. After 72 hours from the treatment, the matrices are extracted with water and the elutriates obtained are treated as described in the method for the determination of anionic surfactants according to the MBAS technique. Finally, the absorption, through a spectrophotometric technique at 650 nm, of the final solution obtained by complexation with molybdenum blue and extraction in chloroform is evaluated. The data obtained by analyzing the soil as it is and the conditioned reference matrix are used as reference values.

Absorption at 650 nm

Reference soil <0.03873>

Reference matrix 0.10500

Treatment 6 0.03622

Treatment 7 0.09271

Treatment 8 <0.01066>

Table 4

The data reported in Table 4 in Figure 2 show that in the absence of a source of Iron (II) ions the oxidative treatment is not promoted, even with very high doses of hydrogen peroxide.

Example 3

Table 5 shows the dosage, expressed as a percentage by weight on the soil, of 5% hydrogen peroxide in concentration and ferrous sulphate heptahydrate used for the treatment of the conditioned soil with anionic surfactant. The conditioned and treated matrix is evaluated at different times (30 minutes, 24 and 72 hours).

Parts by weight referred to

amount of soil (%)

Treatment 9

Hydrogen peroxide 5% 3.87

Ferrous sulphate heptahydrate 0.63

Water <16.70>

Table 5: composition of the treatment

The matrices to be treated are prepared by adding 85 mg of sodium laurethoxy sulfate and 167 g of water to each kilogram of reference medium. To obtain homogeneous and conditioned matrices, they are mixed with a mechanical stirrer. These conditioned matrices are treated with the same quantity of hydrogen peroxide (5% concentration) and ferrous sulphate heptahydrate. The matrices are extracted with water after 30 minutes, 24 and 72 hours and the eluates obtained are treated as described in the method for the determination of anionic surfactants according to the MBAS technique. Finally, the absorption, through a spectrophotometric technique at 650 nm, of the final solution obtained by complexation with molybdenum blue and extraction in chloroform (MBAS method) is evaluated. The data obtained by analyzing the soil as it is and the conditioned reference matrix are used as reference values.

Absorption a

650 nm

Reference soil <0.03873>

Reference matrix 0.10500

Treatment 9 (30 min) <0.03620>

Treatment 9 (24 hours) <0.03449>

Treatment 9 (72 hours) <0.03100>

Table 6

The data shown in Table 6 and Figure 3 show that treatment No. 9 leads to a significant reduction in absorption immediately after 30 minutes from the addition of hydrogen peroxide and ferrous sulphate.

Example 4

Table 7 shows the dosages, expressed as a percentage by weight on the soil, of hydrogen peroxide at 5% in concentration and ferrous sulphate heptahydrate used for the treatment of soil conditioned with anionic surfactant.

Parts by weight referred to the quantity of soil (%)

Treatment Treatment Treatment Treatment Treatment 10 11 12 13 14

Water 1.60 2.00 1.60 2.00 6.00

oxygenated

5%

Sulphate 0.50 0.50 0.30 0.62 1.00

ferrous

heptahydrate

Water 100 100 100 100 100

Table 7: composition of treatments

The reference matrix is a soil from a storage site. The surfactant within this matrix was persistent and non-biodegradable. This conditioned matrix was treated with different dosages of hydrogen peroxide (concentration 5%) and ferrous sulphate heptahydrate. After 24 hours from the treatment, the matrices are extracted with water and the elutriates obtained are treated as described in the method for the determination of anionic surfactants according to the MBAS technique. Finally, the absorption, through a spectrophotometric technique at 650 nm, of the final solution obtained by complexation with molybdenum blue and extraction in chloroform (MBAS method) is evaluated. The amount of surfactant inside the matrix coming from the construction site is used as a reference value.

Surfactants Surfactants Non-ionic cationic anionic surfactants (mg / kg) (mg / kg) (mg / kg) Conditioned matrix <70 <16 <210>

Treatment 10 25 <3.3 <6.6

Treatment 11 24 <6.2 <6.2

Treatment 12 19 <5.9 <5.9

Treatment 13 17 <2.8 <5.6

Treatment 14 28 <3.4 <6.8

Table 8: concentrations expressed in mg of surfactant on kg of soil The data reported in table 8 show that the treatments lead to a significant reduction in the anionic surfactant concentrations.

Example 5

Table 9 shows the dosages, expressed as a percentage by weight on the soil, of hydrogen peroxide at 5% in concentration and ferrous sulphate heptahydrate used for the treatment of soil conditioned with anionic surfactant.

Parts by weight referred to the quantity of soil (%)

Treatment Treatment Treatment

15 16 17

Hydrogen peroxide 2.60 1.60 0.80

5%

Ferrous sulphate 0.43 0.27 0.13 heptahydrate

Water 15.00 15.00 15.00

Table 9: composition of treatments

The reference conditioned matrices to be processed are prepared

adding 110 mg of sodium laurylethoxy sulfate and 150 g of water on each

kilogram of land. The laurylethoxy sulfate used in these examples is

characterized by an ethoxylation number equal to 2. To obtain

Homogeneous and conditioned matrices are mixed with a mechanical stirrer.

These conditioned reference matrices are treated with quantities

variables of hydrogen peroxide (5% concentration) and ferrous sulphate heptahydrate.

After 24 hours from the treatment the matrices are extracted and the elutrates obtained

are evaluated with the HPLC-MS method (high liquid chromatography

performance coupled to a mass detector). It is used as

reference value the quantity of surfactant, determined at 24 hours,

within the conditioned and untreated matrix.

Sodium laurethoxy

2EO sulfate

(mg / kg)

Conditioned matrix 97.7

Treatment 15 24.5

Treatment 16 <32.0>

Treatment 17 91.1

Table 10: concentrations expressed in mg of surfactant per kg of soil

The data reported in table 10 show that the treatments lead to one

reduction of anionic surfactant concentrations in correlation to

concentration of the treatment.

Example 6

Table 11 shows the dosages, expressed as a percentage by weight

on the ground, 5% hydrogen peroxide in concentration and ferrous sulphate

heptahydrate used for the treatment of conditioned medium with anionic surfactant.

Parts by weight referred to the quantity of soil (%)

Treatment Treatment Treatment

15 16 17

Hydrogen peroxide 2.60 1.60 0.80

5%

Ferrous sulphate 0.43 0.27 0.13 heptahydrate

Water 15.00 15.00 15.00

Table 11: composition of treatments

The reference conditioned matrices to be treated are prepared by adding 110 mg of sodium laurylethoxy sulfate and 150 g of water to each kilogram of medium. The laurethoxy sulfate used in these examples is characterized by an ethoxylation number equal to 7. To obtain homogeneous and conditioned matrices, they are mixed with a mechanical stirrer. These conditioned reference matrices are treated with variable quantities of hydrogen peroxide (5% concentration) and ferrous sulphate heptahydrate. After 24 hours from the treatment the matrices are extracted and the elutrates obtained are evaluated with the HPLC-MS method (high performance liquid chromatography coupled to a mass detector). The amount of surfactant, determined at 24 hours, within the matrix conditioned with the surfactant and not treated is used as a reference value.

Sodium laurethoxy sulfate 7EO (mg / kg)

Conditional matrix 110

Treatment 15 7.0

Treatment 16 20.2

Treatment 17 28.4

Table 12: concentrations expressed in mg of surfactant per kg of soil The data reported in table 12 show that the treatments lead to a significant reduction in the anionic surfactant concentrations. The surfactant characterized by an ethoxylation number equal to 7 was found to be more degradable with the proposed treatment.

Claims (10)

CLAIMS 1. A method for reducing the content of organic compounds in the excavated soil through mechanical cutters for the construction of tunnels and shafts which includes the addition of hydrogen peroxide in the presence of Fe (II) ions to the soil on the excavation face and / or in the conditioning chamber and / or in the extractive screw and / or on the conveyor belt and / or on the conveyor wagons or on the stored soil deriving from mechanized excavation in milling machines and wells. 2. A method according to claim 1 in which the hydrogen peroxide is added in percentages by weight from 0.10 to 15.00% expressed as a percentage by weight of hydrogen peroxide at 5% concentration on the amount of soil to be treated. 3. A method according to claim 1 or 2 in which the Fe (II) ions are added as ferrous sulfate heptahydrate or ferrous sulfate in aqueous solution. 4. A method according to claim 3 wherein the ferrous sulphate is added in percentages by weight from 0.01 to 10.00% expressed as a percentage by weight of ferrous sulphate heptahydrate on the amount of soil to be treated. 5. A method according to one or more of claims 1 to 4 wherein the organic compounds comprise foaming surfactants of anionic, cationic and non-ionic nature. A method according to claim 5 wherein the surfactant is anionic. 7. A method according to claim 6 wherein the anionic surfactant is an alkyl sulfate or lauryl sulfate salt. A method according to claim 6 wherein the alkyl sulfate or lauryl sulfate salt is characterized by an ethoxylation number of 7. A method according to claim 8 wherein the salt is the sodium salt. 10. Use of hydrogen peroxide and iron (II) salts to reduce the content of organic compounds in the excavated soil by means of mechanical drills for the construction of tunnels and wells. Milan, 15 September 2016